Who drinks with whom when? Drinking and reciprocity

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Members of some social groups keep spirits high by taking turns hosting events or buying the next rounds of drinks. SFI Omidyar Fellow Paul Hooper, SFI Research Fellow Simon DeDeo, and their collaborators recently explored how patterns of reciprocity vary with people's geographic and genetic closeness by analyzing who drinks with whom, and when.

Read the article in the Albuquerque Journal (February 13, 2014)

Their study was published November 13, 2013 in the journal Entropy.

Evolutionary biology holds that social relationships can form in a number of ways. One is by virtue of kinship: related organisms, be they slime molds or baboons, have a shared interest in keeping their shared genes going, explains Hooper. Another is simple reciprocity: where kindness is repaid, evolution favors the bond of friendship.

During a research trip in Bolivia, Hooper, an evolutionary anthropologist, and his partner Ann Hooper Caldwell looked at how reciprocity varied with kinship and distance based on a favorite local pastime. Families in villages throughout South and Central America frequently host parties where friends and relatives gather to socialize over rounds of chicha, a lightly alcoholic beer. By peeling and boiling sweet manioc (a starchy tuber), then chewing boiled pieces to introduce enzymes, women prepare jugs of it every few days.

The pair interviewed households of a small Amazonian village of the indigenous Tsimane' tribe twice a week over four months to see who hosted whom at chicha parties, and how often the favor was repaid.

Using computational analysis techniques developed by DeDeo, the team found that the more related the households, the more often they drank together at chicha parties. (As relatedness is also a determinant of living proximity, an indirect effect of kinship emerges where a household ends up partying with neighbors who tend to be kin.)

The study, “Dynamical Structure of a Traditional Amazonian Social Network,” also found a reciprocity signature among friends and distant relations: one family hosting another doubles the chance the second will host the first within three days. Hooper explains that rules of etiquette appear to apply to more distant bonds, as it's polite to return the favor promptly, but closer relations don't keep such score.

"It's a clear test of the theory of reciprocity, which has been beset by a lot of doubt since it was introduced in early seventies," says Hooper. The study's novel analyses make the findings particularly robust and offer new methods for future studies, he notes.

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